1. Technical Field
The present invention relates to an electro-optic device such as an organic electro luminescent (EL) device and a method of manufacturing the device.
2. Related Art
In general, an organic EL element included in an organic EL device has a structure having a thin film of a light emitting organic material formed between an anode and a cathode. And it is understood that electrons and positive holes injected from the both electrodes are recombined in the light emitting layer to discharge the excited energy as emission of light.
In such an organic EL element, in order for forming a film of an organic material such as a light emitting layer or a carrier transport layer, a vacuum evaporation method or a coating method is mainly adopted.
In the evaporation method, the masked vacuum evaporation method is used for fine patterning, but because of the problem of the mask distortion, it is allegedly difficult in general to obtain high patterning accuracy in manufacturing large-screen displays.
Meanwhile in the coating method, for example, an inkjet method for selectively ejecting droplets is used for fine patterning, which can be applied to manufacturing the large-screen display with relative ease. Further, since the material is disposed only to necessary portions, improvement in efficiency of material use can also be expected.
Note that the organic EL element manufactured by the coating method is reported in, for example, J. H. Burroughs, D. D. C., Bradley, A. R. Brown, R. N. Marks, R. H. Friend, P. L. Burns, A. B., Holmes, Nature, 347, 539 (1990).
In general, it is known in the organic EL element that element characteristics such as quantum efficiency in light emission or life can be improved by forming a carrier injection layer or a carrier transport layer between the light emitting layer for emitting light and the electrode.
For example, JP-A-10-92584 (Application Number: Hei-9-187137) reports that the element characteristics can be improved by inserting the conductive polymer composed of PEDOT/PSS (polyethelenedioxithiophene/polystyrene-sulfonic-acid) between ITO and the light emitting layer as a hole injection layer.
However, the carrier injection layer and the carrier transport layer might cause degradation in the emission efficiency or the life. For example, in the case in which the PEDOT/PSS is utilized as the material of the hole injection layer, the problem of degradation in the emission efficiency and the life caused by dispersion of chemical species in the light emitting layer has arisen. Further, the problem has also arisen that imbalance between transferring speeds of electron and positive hole increases probability of collision between electron and positive hole in other areas than the light emitting layer to increase the ineffective current, thus degrading the emission efficiency.